An endoscopic system is a system for observing or treating the internal portion of body cavities by inserting an endoscope comprising an imaging system into body cavities of a subject. An endoscopic system is used for observation and/or treatment of, for example, sites such as the bronchi, the esophagus, or the large intestine.
Additionally, it is possible to generate virtual endoscopic images (hereinafter may be referred to as “virtual endoscopic image”) using medical image data obtained by medical image diagnosis systems such as X-ray CT systems and/or MRI systems (magnetic resonance imaging systems). These virtual endoscopic images are used for aiding endoscope operation at the time of examination or treatment using an endoscopic system and have a complementary function of endoscopic images. For example, at the time of examination or treatment using an endoscopic system, an endoscopic image obtained in real time and a virtual endoscopic image are displayed side by side (for example, Japanese published unexamined application No. 2005-21355). In this case, the position of a viewpoint and a view direction are matched on both images to display the endoscopic image and virtual endoscopic image side by side. Furthermore, it is possible to effectively perform observation using the endoscopic image by superimposing and displaying the results through a CAD (Computer Aided Diagnosis) on the virtual endoscopic image.
By displaying the endoscopic image and virtual endoscopic image side by side, it is possible to effectively perform observation using the endoscopic image while advancing an endoscope within a body cavity of a subject. On the other hand, with regard to observation using an endoscopic system, observation may be performed by advancing the endoscope and by retracting the endoscope. This is because observation by advancing the endoscope may cause perforation; therefore, observation by retracting it is safer.
When an endoscopic image and virtual endoscopic image are displayed, the view directions of each image are also matched. When an endoscopic image and virtual endoscopic image are displayed by retracting an endoscope, the view direction of the virtual endoscopic image faces the opposite direction from the traveling direction of the endoscope. The virtual endoscopic image generated according to this view direction does not show an image facing toward the traveling direction of the endoscope. Therefore, there is a problem in which it is impossible to operate the endoscope while confirming the traveling direction of the endoscope using a virtual endoscopic image.
On the other hand, methods for generating and displaying virtual endoscopic images having the opposite direction from the view direction of an endoscopic image as a view direction have been proposed (for example, Japanese published unexamined application No. H 9-81787). In this case, a field of vision such as a rearview mirror can be obtained. However, since the view directions are opposite direction between the endoscopic image and virtual endoscopic image, it is not easy to intuitively understand a correspondence relationship with the endoscopic image on the virtual endoscopic image.
Moreover, even in the case of advancing an endoscope within the body cavities of a subject, a viewpoint of the virtual endoscopic image is set to the tip position of the endoscope. Therefore, it is impossible to fully assure a field of vision of the traveling direction of the endoscope on the virtual endoscopic images generated according to that viewpoint, and this may cause perforation.